Process for rendering metal corrosion-resistant in electrochemical metal deposition

ABSTRACT

A new and improved method for electroplating a metal onto a substrate in such a manner as to render the metal essentially corrosion-resistant during subsequent substrate processing such as chemical mechanical polishing. The process involves incorporating nitrogen into the metal as the metal is electroplated onto the substrate. The process includes preparing the electroplating bath, placing a leveler chemical containing nitrogen in the prepared bath, circulating the leveler chemical throughout the bath and then electroplating the metal on the substrate. In a preferred embodiment, alkyl polyamide, alkyl amine, alkyl amine oxide or thiourea with molecular weight ranging from 100˜1,000,000 is used as the leveler chemical.

FIELD OF THE INVENTION

The present invention relates to electroplating systems used in the deposition of metal layers on semiconductor wafer substrates in the fabrication of semiconductor integrated circuits. More particularly, the present invention relates to a process for electroplating a corrosion-resistant metal such as copper on a substrate in electrochemical metal deposition.

BACKGROUND OF THE INVENTION

In the fabrication of semiconductor integrated circuits, metal conductor lines are used to interconnect the multiple components in device circuits on a semiconductor wafer. A general process used in the deposition of metal conductor line patterns on semiconductor wafers includes deposition of a conducting layer on the silicon wafer substrate; formation of a photoresist or other mask such as titanium oxide or silicon oxide, in the form of the desired metal conductor line pattern, using standard lithographic techniques; subjecting the wafer substrate to a dry etching process to remove the conducting layer from the areas not covered by the mask, thereby leaving the metal layer in the form of the masked conductor line pattern; and removing the mask layer typically using reactive plasma and chlorine gas, thereby exposing the top surface of the metal conductor lines. Typically, multiple alternating layers of electrically conductive and insulative materials are sequentially deposited on the wafer substrate, and conductive layers at different levels on the wafer may be electrically connected to each other by etching vias, or openings, in the insulative layers and filling the vias using aluminum, tungsten or other metal to establish electrical connection between the conductive layers.

Deposition of conductive layers on the wafer substrate can be carried out using any of a variety of techniques. These include oxidation, LPCVD (low-pressure chemical vapor deposition), APCVD (atmospheric-pressure chemical vapor deposition), and PECVD (plasma-enhanced chemical vapor deposition). In general, chemical vapor deposition involves reacting vapor-phase chemicals that contain the required deposition constituents with each other to form a nonvolatile film on the wafer substrate. Chemical vapor deposition is the most widely-used method of depositing films on wafer substrates in the fabrication of integrated circuits on the substrates.

Due to the ever-decreasing size of semiconductor components and the ever-increasing density of integrated circuits on a wafer, the complexity of interconnecting the components in the circuits requires that the fabrication processes used to define the metal conductor line interconnect patterns be subjected to precise dimensional control. Advances in lithography and masking techniques and dry etching processes, such as RIE (Reactive Ion Etching) and other plasma etching processes, allow production of conducting patterns with widths and spacings in the submicron range. Electrodeposition or electroplating of metals on wafer substrates has recently been identified as a promising technique for depositing conductive layers on the substrates in the manufacture of integrated circuits and flat panel displays. Such electrodeposition processes have been used to achieve deposition of the copper or other metal layer with a smooth, level or uniform top surface. Consequently, much effort is currently focused on the design of electroplating hardware and chemistry to achieve high-quality films or layers which are uniform across the entire surface of the substrates and which are capable of filling or conforming to very small device features. Copper has been found to be particularly advantageous as an electroplating metal.

Electroplated copper provides several advantages over electroplated aluminum when used in integrated circuit (IC) applications. Copper is less electrically resistive than aluminum and is thus capable of higher frequencies of operation. Furthermore, copper is more resistant to electromigration (EM) than is aluminum. This provides an overall enhancement in the reliability of semiconductor devices because circuits which have higher current densities and/or lower resistance to EM have a tendency to develop voids or open circuits in their metallic interconnects. These voids or open circuits may cause device failure or burn-in.

FIG. 1 schematically illustrates a typical standard or conventional electroplating system 10 for depositing copper onto a semiconductor wafer 18. The electroplating system 10 includes a standard electroplating cell having an adjustable current source 12, a bath container 14, a copper anode 16 and a cathode 18, which cathode 18 is the semiconductor wafer that is to be electroplated with copper. The anode 16 and semiconductor wafer/cathode 18 are connected to the current source 12 by means of suitable wiring 38. The bath container 14 holds a bath 20 typically of acid copper sulfate (CuSO₄) solution which may include an additive for filling of submicron features and leveling the surface of the copper electroplated on the wafer 18.

As illustrated in FIGS. 1 and 2, the electroplating system 10 typically further includes a pair of bypass filter conduits 24 which extend through the anode 16 and open to the upper, oxidizing surface 22 of the anode 16 through respective sludge openings 26 at opposite ends of the anode 16. The bypass filter conduits 24 connect to a bypass pump/filter 30 located outside the bath container 14, and the bypass pump/filter 30 is further connected to an electrolyte holding tank 34 through a tank inlet line 32. The electrolyte holding tank 34 is, in turn, connected to the bath container 14 through a tank outlet line 36. The electrolyte content of the bath 20 can be increased, as needed, by adding electrolytes to the electrolyte holding tank 34 and then circulating the bath 20 through the bypass filter conduits 24, the bypass pump/filter 30, the tank inlet line 32, the electrolyte holding tank 34 and back into the bath container 14 through the tank outlet line 36, respectively.

In operation of the electroplating system 10, the current source 12 applies a selected voltage potential typically at room temperature between the anode 16 and the cathode/wafer 18. This potential creates a electrical field around the anode 16 and the cathode/wafer 18, which electrical field affects the distribution of the copper ions in the bath 20. In a typical copper electroplating application, a voltage potential may be applied s, and a current flows between the anode 16 and the cathode/wafer 18. Consequently, copper is oxidized typically at the oxidizing surface 22 of the anode 16 as electrons from the copper anode 16 and reduce the ionic copper in the copper sulfate solution bath 20 to form a copper electroplate (not illustrated) at the interface between the cathode/wafer 18 and the copper sulfate bath 20.

The copper oxidation reaction which takes place at the oxidizing surface 22 of the anode 16 is illustrated by the following reaction formula (1): Cu---->Cu⁺⁺+2e−  (1)

The oxidized copper cation reaction product forms ionic copper sulfate in solution with the sulfate anion in the bath 20: Cu⁺⁺+SO₄ ⁻⁻---->Cu⁺⁺SO₄ ⁻⁻  (2)

At the cathode/wafer 18, the electrons harvested from the anode 16 flowed through the wiring 38 reduce copper cations in solution in the copper sulfate bath 20 to electroplate the reduced copper onto the cathode/wafer 18: Cu⁺⁺+2e−---->Cu  (3)

As the anode 16 is consumed during the electroplating process, small quantities of solid copper sulfate or “anode fines” tend to precipitate at the interface between the copper sulfate bath 20 and the oxidizing surface 22 of the anode 16 to form a copper precipitate or sludge 28 on the oxidizing surface 22, as illustrated in FIG. 2.

After the copper is electroplated onto the wafer 18, the wafer 18 is frequently subjected to a CMP (chemical mechanical polishing) process to smooth the surface of the electroplated copper layer. Important components used in CMP processes include an automated rotating polishing platen and a wafer holder, which both exert a pressure on the wafer and rotate the wafer independently of the platen. The polishing or removal of surface layers is accomplished by a polishing slurry consisting mainly of colloidal silica suspended in deionixed water or KOH solution. The slurry is frequently fed by an automatic slurry feeding system in order to ensure uniform wetting of the polishing pad and proper delivery and recovery of the slurry. For a high-volume wafer fabrication process, automated wafer loading/unloading and a cassette handler are also included in a CMP apparatus.

As the name implies, a CMP process executes a microscopic action of polishing by both chemical and mechanical means. While the exact mechanism for material removal of an oxide layer is not known, it is hypothesized that the surface layer of silicon oxide is removed by a series of chemical reactions which involve the formation of hydrogen bonds with the oxide surface of both the wafer and the slurry particles in a hydrogenation reaction; the formation of hydrogen bonds between the wafer and the slurry; the formation of molecular bonds between the wafer and the slurry; and finally, the breaking of the oxide bond with the wafer or the slurry surface when the slurry particle moves away from the wafer surface. It is generally recognized that the CMP polishing process is not a mechanical abrasion process of slurry against a wafer surface.

One of the problems which is inherent in the conventional electroplating process is that the electroplated copper has a tendency to corrode after it is subjected to chemical mechanical polishing. The corrosion is manifested by small pits in the copper and can adversely affect the yield of devices fabricated on the wafer. Accordingly, a process is needed for rendering copper or other metal corrosion-resistant as it is electroplated onto a wafer substrate, to prevent corrosion of the metal during subsequent chemical mechanical polishing or other processing.

An object of the present invention is to provide a new and improved process for electroplating a metal on a substrate.

Another object of the present invention is to provide a new and improved process for electroplating a corrosion-resistant metal on a substrate.

Still another object of the present invention is to provide a new and improved process for rendering an electroplating metal corrosion-resistant by incorporating nitrogen into the metal.

Yet another object of the present invention is to provide a new and improved process which is applicable to electroplating copper or any of a variety of other metals on a substrate.

A still further object of the present invention is to provide a new and improved process which is applicable to preventing corrosion of an electroplated metal such as copper on a substrate after chemical mechanical polishing of the metal.

Another object of the present invention is to provide a process for electroplating a corrosion-resistant metal on a substrate, including providing a nitrogen-containing leveler chemical in an electroplating bath prior to electroplating the metal on the substrate.

SUMMARY OF THE INVENTION

In accordance with these and other objects and advantages, the present invention is generally directed to a new and improved method for electroplating a metal onto a substrate in such a manner as to render the metal essentially corrosion-resistant during subsequent substrate processing such as chemical mechanical polishing. The process involves incorporating nitrogen into the metal as the metal is electroplated onto the substrate. The process includes preparing the electroplating bath, placing a leveler chemical containing nitrogen in the prepared bath, circulating the leveler chemical throughout the bath and then electroplating the metal on the substrate. In a preferred embodiment, alkyl polyamide, alkyl amine, alkyl amine oxide or thiourea with molecular weight ranging from 100˜1,000,000 is used as the leveler chemical.

The leveler chemical is typically circulated throughout the bath. Typical concentrations of nitrogen incorporated into the copper may range from about 0.1 ppm to about 1000 ppm. Due to the amine and phenyl groups present in the leveler chemical, the copper film deposited onto the substrate is resistant to corrosion particularly during a chemical mechanical polishing process following the electroplating process.

The process of the present invention may be used with any electroplating bath formulation, such as copper, aluminum, nickel, chromium, zinc, tin, gold, silver, lead and cadmium plating baths. Plating baths containing mixtures of metals to be plated are also contemplated by the present invention. It is preferred that the plating bath be a copper or copper-alloy electroplating bath, and more preferably, a copper electroplating bath.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic of a typical conventional electroplating system suitable for implementation of the present invention;

FIG. 2 is a side view of a typical conventional anode used in an electroplating process;

FIG. 3 is a schematic of an electroplating system in implementation of the present invention;

FIG. 4 is a cross-sectional view of a substrate with a corrosion-resistant layer of metal electroplated thereon in accordance with the process of the present invention; and

FIG. 5 is a flow diagram summarizing typical sequential process steps in implementation of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention has particularly beneficial utility in electroplating copper on a semiconductor wafer substrate in the fabrication of integrated circuits on the substrate. However, the invention is more generally applicable to electroplating copper or other metals such as aluminum, nickel, chromium, zinc, tin, gold, silver, lead and cadmium on substrates in a variety of mechanical and industrial applications. The present invention is also applicable to electroplating alloys of metals on substrates.

The process includes circulating a leveler chemical containing amine and phenyl groups in an electroplating bath prior to electroplating the metal on the substrate. Nitrogen from the leveler chemical is incorporated into the metal as the metal is electroplated onto the substrate, such that the electroplated metal is substantially corrosion-resistant. The process is particularly advantageous in preventing or substantially reducing or eliminating corrosion of the metal during a subsequent chemical mechanical polishing process.

According to a preferred embodiment, the nitrogen-containing leveler chemical is alkyl polyamide, alkyl amine, alkyl amine oxide or thiourea, with molecular weight ranging from 100˜1,000,000. Briefly, after the electroplating bath is prepared the leveler chemical is added to the bath at a concentration of typically 0.1 ppm to 1000 ppm. Finally, as the metal is electroplated onto the substrate, nitrogen from the leveler chemical is incorporated into the metal to render the metal substantially resistant to corrosion during subsequent processing. The leveler chemical in the electroplating bath facilitates incorporation of nitrogen into the electroplated metal in a concentration of typically from about 0.1 ppm to about 1000 ppm.

The process of the invention may be used with any electroplating bath formulation, such as copper, aluminum, nickel, chromium, zinc, tin, gold, silver, lead and cadmium electroplating baths. The present invention also contemplates the use of electroplating baths containing mixtures of metals to be plated onto a substrate. It is preferred that the electroplating bath be a copper alloy electroplating bath, and more preferably, a copper electroplating bath. Typical copper electroplating bath formulations are well known to those skilled in the art and include, but are not limited to, an electrolyte and one or more sources of copper ions. Suitable electrolytes include, but are not limited to, sulfuric acid, acetic acid, fluoroboric acid, methane sulfonic acid, ethane sulfonic acid, trifluormethane sulfonic acid, phenyl sulfonic acid, methyl sulfonic acid, p-toluenesulfonic acid, hydrochloric acid, phosphoric acid and the like. The acids are typically present in the bath in a concentration in the range of from about 1 to about 300 g/L. The acids may further include a source of halide ions such as chloride ions. Suitable sources of copper ions include, but are not limited to, copper sulfate, copper chloride, copper acetate, copper nitrate, copper fluoroborate, copper methane sulfonate, copper phenyl sulfonate and copper p-toluene sulfonate. Such copper ions sources are typically present in a concentration in the range of from about 5 to about 300 g/L of electroplating solution.

Referring to FIG. 3, a schematic of an electroplating system 40 which is suitable for implementation of the present invention is shown. The electroplating system 40 typically includes a bath container 44 in which a typically copper anode 46 and a cathode 48 are placed, the cathode 48 being the semiconductor wafer that is to be electroplated with copper. An adjustable current source 42 is connected to the anode 46 and to the semiconductor wafer/cathode 48 through suitable wiring 68. The bath container 44 holds an electroplating bath 50 typically of acid copper sulfate (CuSO₄) solution, for example, which may include an additive for filling of submicron features and leveling the surface of the copper electroplated on the wafer 48, as is known by those skilled in the art. A pair of bypass filter conduits 54 extends through the anode 46 and each opens to the upper, oxidizing surface of the anode 46. A bypass pump/filter 60 located outside the bath container 44 is connected to the bypass filter conduits 54, and an electrolyte holding tank 64 is connected to the bypass pump/filter 60 through a tank inlet line 62. A tank outlet line 66 in turn connects the electrolyte holding tank 64 to the bath container 44. The electrolyte content of the bath 50 can be increased, as needed, by adding electrolytes to the electrolyte holding tank 64 and then circulating the bath 50 through the bypass filter conduits 54, the bypass pump/filter 60, the tank inlet line 62, the electrolyte holding tank 64 and back into the bath container 44 through the tank outlet line 66, respectively.

In accordance with the process of the present invention, the electroplating metal bath 50, typically including CuSO₄, is first prepared in the bath container 44. As shown in FIG. 3, a leveler chemical 70, preferably alkyl polyamide, alkyl amine, alkyl amine oxide, thiourea, with molecular weight ranging from 100˜1,000,000 is poured into the bath 50. In a preferred embodiment, the leveler chemical 70 is present in the bath 50 in a concentration of 0.1 ppm to 1000 ppm. This concentration of the leveler chemical 70 in the electroplating bath 50 facilitates incorporation of nitrogen into the electroplated metal in a concentration of from about 0.1 ppm to about 1000 ppm. After the desired concentration of the leveler chemical 70 is added to the bath 50, the leveler chemical 70 is circulated from the bath container 44 through the bypass filter conduits 54 and then through the bypass pump/filter 60, the tank inlet line 62, the electrolyte holding tank 64, the tank outlet line 66 and back into the bath container 44, respectively.

Referring next to FIGS. 3 and 4, after the leveler chemical 70 is thoroughly mixed in the electroplating bath 50 typically in the manner heretofore described, the electroplating system 40 is operated typically in conventional fashion to electroplate the metal from the metal electrolyte solution in the bath 50, onto the substrate 48. Accordingly, the current source 42 applies a selected voltage potential typically at room temperature between the anode 46 and the cathode/wafer 48. This potential creates a electrical field around the anode 46 and the cathode/wafer 48, which electrical field affects the distribution of the metal ions in the bath 50. In a typical copper electroplating application, a voltage potential of about 2 volts may be applied for about 2 minutes, and a current of about 4.5 amps flows between the anode 46 and the cathode/wafer 48. Consequently, the metal is oxidized typically at the upper oxidizing surface of the anode 46 as electrons from the metal anode 46 reduce the ionic metal in the electrolyte solution bath 50 to form a substantially corrosion-resistant electroplated metal layer 72, as shown in FIG. 4, at the interface between the cathode/wafer 48 and the electrolyte bath 50. As a result of the presence of the leveler chemical 70 in the electroplating bath 50, nitrogen atoms are incorporated into the metal layer 72 typically at a concentration of from about 0.1 to about 1000 ppm. Accordingly, upon subsequent processing of the substrate 48, such as during chemical mechanical polishing, the metal layer 72 resists corrosion and the accompanying formation of pits therein which otherwise would adversely affect the yield of devices fabricated on the substrate 48.

Referring next to the flow diagram of FIG. 5, typical process steps for carrying out the present invention are shown. In process step S1, the metal electrolyte bath is prepared typically using copper. Other metals which may be used include aluminum, nickel, chromium, zinc, tin, gold, silver, lead and cadmium. In process step S2, the leveler chemical is added to the prepared electrolyte bath. In process step S3, the leveler chemical is circulated in the electrolyte bath In process step S4, the metal in the electrolyte bath is electroplated with nitrogen atoms from the leveler chemical onto the substrate to form the corrosion-resistant, nitrogen-enriched electroplated metal layer thereon.

While the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications can be made in the invention and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention. 

1. A process for electroplating a substrate, comprising the steps of: providing an electrolyte bath comprising a metal; mixing a nitrogen-containing leveler chemical with said electrolyte bath; electroplating said metal onto said substrate; and subjecting said metal to chemical mechanical planarization.
 2. The process of claim 1 wherein said leveler chemical comprises a leveler chemical selected from the group consisting of alkyl polyamide, alkyl amine, alkyl amine oxide and thiourea having a molecular weight ranging from 100˜1,000,000.
 3. The process of claim 1 wherein said metal comprises copper.
 4. The process of claim 3 wherein said leveler chemical comprises a leveler chemical selected from the group consisting of alkyl polyamide, alkyl amine, alkyl amine oxide and thiourea having a molecular weight ranging from 100˜1,000,000.
 5. The process of claim 1 wherein said metal is a copper alloy.
 6. The process of claim 5 wherein said leveler chemical comprises a leveler chemical selected from the group consisting of alkyl polyamide, alkyl amine, alkyl amine oxide and thiourea having a molecular weight ranging from 100˜1,000,000.
 7. The process of claim 1 wherein said metal is a metal selected from the group consisting of copper, aluminum, nickel, chromium, zinc, tin, gold, silver, lead and cadmium.
 8. The process of claim 7 wherein said leveler chemical comprises a leveler chemical selected from the group consisting of alkyl polyamide, alkyl amine, alkyl amine oxide and thiourea having a molecular weight ranging from 100˜1,000,000.
 9. A process for providing a substantially corrosion-resistant metal layer on a substrate, comprising the steps of: providing an electrolyte bath comprising a metal; mixing a nitrogen-containing leveler chemical with said electrolyte bath; and incorporating nitrogen from said leveler chemical into said metal and providing said metal on the substrate by electroplating said metal onto the substrate.
 10. The process of claim 9 wherein said leveler chemical comprises a leveler chemical selected from the group consisting of alkyl polyamide, alkyl amine, alkyl amine oxide and thiourea having a molecular weight ranging from 100˜1,000,000.
 11. The process of claim 9 wherein said metal comprises copper.
 12. The process of claim 11 wherein said leveler chemical comprises a leveler chemical selected from the group consisting of alkyl polyamide, alkyl amine, alkyl amine oxide and thiourea having a molecular weight ranging from 100˜1,000,000.
 13. The process of claim 9 wherein said metal is a copper alloy.
 14. The process of claim 13 wherein said leveler chemical comprises a leveler chemical selected from the group consisting of alkyl polyamide, alkyl amine, alkyl amine oxide and thiourea, having a molecular weight ranging from 100˜1,000,000.
 15. The process of claim 9 wherein said nitrogen is present in said metal in a concentration of from about 10 ppm to about 1000 ppm.
 16. The process of claim 15 wherein said metal is a metal selected from the group consisting of copper, aluminum, nickel, chromium, zinc, tin, gold, silver, lead and cadmium.
 17. A process for providing a substantially corrosion-resistant metal layer on a substrate, comprising the steps of: providing an electrolyte bath comprising a metal; mixing a nitrogen-containing leveler chemical with said electrolyte bath; and incorporating nitrogen from said leveler chemical into said metal at a nitrogen concentration of from about 10 ppm to about 1000 ppm and providing said metal on the substrate by electroplating said metal onto the substrate.
 18. The process of claim 17 wherein said leveler chemical comprises a leveler chemical selected from the group consisting of alkyl polyamide, alkyl amine, alkyl amine oxide and thiourea having a molecular weight ranging from 100˜1,000,000.
 19. The process of claim 17 wherein said metal is a copper alloy.
 20. The process of claim 17 wherein said metal is a metal selected from the group consisting of copper, aluminum, nickel, chromium, zinc, tin, gold, silver, lead and cadmium. 